1. Technical Field
The present invention relates to a laser beam source device, a projector, and a monitoring device, and more particularly to a laser beam source device capable of producing high output.
2. Related Art
A high-pressure mercury lamp has been often used as an illumination light source of an optical apparatus such as a projector. However, the high-pressure mercury lamp has several problems such as limited color reproducibility, insufficient rapidity in lighting, and short life. For solving these problems, a laser beam source device applicable in this field has been under development. Particularly, a laser beam source device having an external resonator structure capable of intensifying light having a particular wavelength by using the external resonator has been developed to produce high output. According to this type of laser beam source device, however, it is difficult to obtain a sufficient amount of light in some cases only by laser beam generation depending on wavelengths of light. Thus, a technology which generates light having a fundamental wavelength such as a infrared laser beam and then converts the infrared laser beam into visible light having a ½ wavelength by using a wavelength converging element such as a second harmonic generator (hereinafter abbreviated as SHG) has been employed.
According to this technology, the laser beam needs to be amplified by successive inductive discharge generated through reciprocation of the laser beam several times within a laser generator. However, when the optical axis of the laser beam deviates even only slightly, sufficient reciprocation of the laser beam cannot be achieved. In this case, lasers cannot be generated. For overcoming this drawback, a method for preventing lowering of alignment accuracy caused by thermal lens effect of a laser excitation medium by using a concaved reflection surface of an external resonating mirror has been proposed (for example, see JP-A-2004-363414). According to the description of this reference, the output laser beam reflected by the concaved reflection surface of the external resonating mirror returns toward the optical axis even when the output laser beam expands or deviates by the thermal lens effect of the laser excitation medium. By this method, sufficient output is expected to be produced.
According to this structure, however, extremely accurate alignment is required between a laser diode and the external resonating mirror in some cases so as to generate sufficient laser generation by using the laser generator having the external resonator structure. In this case, there is a possibility that sufficient alignment accuracy cannot be secured when the method disclosed in JP-A-2004-363414 is employed. In addition, the necessity for high alignment accuracy becomes an obstacle to stable manufacture of a low-cost laser beam source device.
Moreover, even when sufficient alignment accuracy is secured between the laser excitation medium and the external resonating mirror by using the laser generator having the external resonator structure, increase in the output of the laser is still limited.